Potentiometric and multinuclear NMR investigations of di-/trimethyltin(iv) cations with some heterocyclic thiones in aqueous media

Abstract

Equilibrium (pH-metric) studies of the interaction of Me₂Sn(IV)²⁺ and Me₃Sn(IV)⁺ with heterocyclic thiones, viz. 5-amino-3H-1,3,4-thiadiazole-2-thione (HL-1), 3-amino-1,2,4-triazole-5-thione (HL-2) and 4-amino-3R-1,2,4-triazole-5-thione (where R = CH₃ (HL-3) and C₂H₅ (HL-4)), in aqueous solution (I = 0.1 M KNO₃, 298 K) were performed. The concentration distribution of the various complex species in solution was evaluated as a function of pH. It was found that these thione ligands (HL) with potential sulfur donor groups interact strongly with Me₂Sn(IV)²⁺ and Me₃Sn(IV)⁺, even at rather acidic pHs < 4.0. The species that exist at physiological pH (7.0) are Me₂SnL(OH) (∼70–85%) and Me₂Sn(OH)₂ (∼15–30%) for dimethyltin(IV) systems, whereas Me₃SnL(OH) (∼73–95%), Me₃SnL (8–24%) and Me₃Sn(OH) (∼1–3%) exist for Me₃Sn(IV)⁺ systems. The complex species formed are water soluble in the pH range 2–10.5. In all of the studied systems, no polymeric species were detected in the experimental pH range. Beyond pH 8.0, significant amounts of hydroxo species, viz. Me₃SnOH and Me₂Sn(OH)₂, were formed. Multinuclear (¹H, ¹³C and ¹¹⁹Sn) NMR studies were also carried out at different pHs in order to characterize the possible geometry of the proposed complex species in aqueous solution.